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docs/acpi/bits: add some clarity and details while also improving formating

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Update bios-bits docs to add more details on why a pre-OS environment for
testing bioses is useful. Add author's FOSDEM talk link. Also improve the
formating of the document while at it.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Ani Sinha 2024-03-08 09:52:52 +05:30 • committed by Michael Tokarev
parent 00691b1f6a
commit d65f1ed7de
1 changed files with 39 additions and 16 deletions
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docs/devel/acpi-bits.rst
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@ -1,26 +1,48 @@
============================================================================= =============================================================================
ACPI/SMBIOS avocado tests using biosbits ACPI/SMBIOS avocado tests using biosbits
============================================================================= =============================================================================
************
Introduction
************
Biosbits is a software written by Josh Triplett that can be downloaded Biosbits is a software written by Josh Triplett that can be downloaded
from https://biosbits.org/. The github codebase can be found from https://biosbits.org/. The github codebase can be found
`here <https://github.com/biosbits/bits/tree/master>`__. It is a software that executes `here <https://github.com/biosbits/bits/tree/master>`__. It is a software that
the bios components such as acpi and smbios tables directly through acpica executes the bios components such as acpi and smbios tables directly through
bios interpreter (a freely available C based library written by Intel, acpica bios interpreter (a freely available C based library written by Intel,
downloadable from https://acpica.org/ and is included with biosbits) without an downloadable from https://acpica.org/ and is included with biosbits) without an
operating system getting involved in between. operating system getting involved in between. Bios-bits has python integration
with grub so actual routines that executes bios components can be written in
python instead of bash-ish (grub's native scripting language).
There are several advantages to directly testing the bios in a real physical There are several advantages to directly testing the bios in a real physical
machine or VM as opposed to indirectly discovering bios issues through the machine or in a VM as opposed to indirectly discovering bios issues through the
operating system. For one thing, the OSes tend to hide bios problems from the operating system (the OS). Operating systems tend to bypass bios problems and
end user. The other is that we have more control of what we wanted to test hide them from the end user. We have more control of what we wanted to test and
and how by directly using acpica interpreter on top of the bios on a running how by being as close to the bios on a running system as possible without a
system. More details on the inspiration for developing biosbits and its real complicated software component such as an operating system coming in between.
life uses can be found in [#a]_ and [#b]_. Another issue is that we cannot exercise bios components such as ACPI and
SMBIOS without being in the highest hardware privilege level, ring 0 for
example in case of x86. Since the OS executes from ring 0 whereas normal user
land software resides in unprivileged ring 3, operating system must be modified
in order to write our test routines that exercise and test the bios. This is
not possible in all cases. Lastly, test frameworks and routines are preferably
written using a high level scripting language such as python. OSes and
OS modules are generally written using low level languages such as C and
low level assembly machine language. Writing test routines in a low level
language makes things more cumbersome. These and other reasons makes using
bios-bits very attractive for testing bioses. More details on the inspiration
for developing biosbits and its real life uses can be found in [#a]_ and [#b]_.
For QEMU, we maintain a fork of bios bits in gitlab along with all the For QEMU, we maintain a fork of bios bits in gitlab along with all the
dependent submodules here: https://gitlab.com/qemu-project/biosbits-bits dependent submodules `here <https://gitlab.com/qemu-project/biosbits-bits>`__.
This fork contains numerous fixes, a newer acpica and changes specific to This fork contains numerous fixes, a newer acpica and changes specific to
running this avocado QEMU tests using bits. The author of this document running this avocado QEMU tests using bits. The author of this document
is the sole maintainer of the QEMU fork of bios bits repo. is the sole maintainer of the QEMU fork of bios bits repository. For more
information, please see author's `FOSDEM talk on this bios-bits based test
framework <https://fosdem.org/2024/schedule/event/fosdem-2024-2262-exercising-qemu-generated-acpi-smbios-tables-using-biosbits-from-within-a-guest-vm-/>`__.
*********************************
Description of the test framework
*********************************
Under the directory ``tests/avocado/``, ``acpi-bits.py`` is a QEMU avocado Under the directory ``tests/avocado/``, ``acpi-bits.py`` is a QEMU avocado
test that drives all this. test that drives all this.
@ -120,8 +142,9 @@ Under ``tests/avocado/`` as the root we have:
(b) Add a SPDX license header. (b) Add a SPDX license header.
(c) Perform modifications to the test. (c) Perform modifications to the test.
Commits (a), (b) and (c) should go under separate commits so that the original Commits (a), (b) and (c) preferably should go under separate commits so that
test script and the changes we have made are separated and clear. the original test script and the changes we have made are separated and
clear. (a) and (b) can sometimes be combined into a single step.
The test framework will then use your modified test script to run the test. The test framework will then use your modified test script to run the test.
No further changes would be needed. Please check the logs to make sure that No further changes would be needed. Please check the logs to make sure that
@ -141,4 +164,4 @@ References:
----------- -----------
.. [#a] https://blog.linuxplumbersconf.org/2011/ocw/system/presentations/867/original/bits.pdf .. [#a] https://blog.linuxplumbersconf.org/2011/ocw/system/presentations/867/original/bits.pdf
.. [#b] https://www.youtube.com/watch?v=36QIepyUuhg .. [#b] https://www.youtube.com/watch?v=36QIepyUuhg
.. [#c] https://fosdem.org/2024/schedule/event/fosdem-2024-2262-exercising-qemu-generated-acpi-smbios-tables-using-biosbits-from-within-a-guest-vm-/